Part:BBa_K5246028
CB2/CB2A HfsK Acetyltransferase, 6xHis tag for purification
Introduction
Vilnius-Lithuania iGEM 2024 project Synhesion aspires to create biodegradable and environmentally friendly adhesives. We were inspired by bacteria, which naturally produce adhesives made from polysaccharides. Two bacteria from aquatic environments - C. crescentus and H. Baltica - harness 12 protein synthesis pathways to produce sugars anchoring them to the surfaces. We aimed to transfer the polysaccharide synthesis pathway to industrially used E. coli bacteria to produce adhesives. Our team concomitantly focused on creating a novel E. coli strain for more efficient production of adhesives.
This protein is part of the Tetrad assembly system BBa_K5246043 and operon responsible for addition of N-acetyl-D-glucosamine and deacetylation BBa_K5246042.
Part was used in Vilnius-Lithuania iGEM 2024 project "Synhesion" https://2024.igem.wiki/vilnius-lithuania/.
This part also has a non 6xhis-tagged variant BBa_K5246012.
Usage and Biology
Caulobacter crescentus is a common freshwater gram-negative oligotrophic bacterium of the clade Caulobacterales. Its distinguishing feature is its dual lifestyle. Initially, C. crescentus daughter cells are in a “swarmer” cell phase, which has a flagellum, enabling them to perform chemotaxis. After the motile phase, they differentiate into “stalked” cells. This phase features a tubular stalk with an adhesive structure called holdfast, allowing them to adhere to surfaces and perform cell division.[1][2]
Caulobacterales synthesize a polysaccharide-based adhesin known as holdfast at one of their cell poles, enabling tight attachment to external surfaces. It is established that holdfast consists of repeating identical units composed of multiple monomers. Current literature agrees that in Caulobacter crescentus, these units form tetrads composed of glucose, an unidentified monosaccharide (either N-mannosamine uronic acid or xylose), N-acetylglucosamine, and N-glucosamine. These units are polymerized and exported to the outer membrane of the cell, where they function as anchors, securing the bacterium to a surface[3][4].
The C. crescentus holdfast is produced via a polysaccharide synthesis and export pathway similar to the group I capsular polysaccharide synthesis Wzy/Wzx-dependent pathway in Escherichia coli.
The holdfast synthesis (hfs) genes include those encoding predicted glycosyltransferases, carbohydrate modification factors, and components of a wzy-type polysaccharide assembly pathway[4][5][6].
HfsK in particular is responsible for deacetylation N-acetylglucosamine.
Sequence and Features
- 10INCOMPATIBLE WITH RFC[10]Illegal PstI site found at 94
- 12INCOMPATIBLE WITH RFC[12]Illegal PstI site found at 94
- 21INCOMPATIBLE WITH RFC[21]Illegal XhoI site found at 823
- 23INCOMPATIBLE WITH RFC[23]Illegal PstI site found at 94
- 25INCOMPATIBLE WITH RFC[25]Illegal PstI site found at 94
- 1000COMPATIBLE WITH RFC[1000]
Experimental characterization
Bioinformatic analysis
Using CDD analysis, it was identified that HfsK is similar to the GNAT N-acetyltransferase family. Its domains suggest that HfsK is part of the Bcls superfamily. Acetyltransferases of this superfamily are usually involved in cellulose biosynthesis. Protein BLAST did not give conclusive results, which could result from a unique HfsK protein amino acid sequence and structure.
DeepTMHMM's protein topology predictions showed that HfsK is most likely a globular protein located on the cytoplasmic side of the membrane.
High confidence scores of AlphaFold 3 structures suggest that HfsK is likely a globular protein. A pTM score above 0.5 suggests that the predicted overall structure may closely resemble the true protein fold, while ipTM indicates the accuracy of the subunit positioning within the complex. Values higher than 0.8 represent confident, high-quality predictions (Fig.1).
To summarise, HfsK is most likely a globular N-acetyltransferase. Earlier evidence, combined with our findings, suggests that it plays a role in the deacetylation of N-acetylglucosamine within the holdfast synthesis pathway. [7][8][9]
Protein expression
<p>We chose the BL21(DE3) strain for adjustable and efficient expression of target proteins since the system's proteins were best expressed in this strain. Given the lack of time, we went with conditions optimized beforehand in earlier experiments for the whole pathway expression: temperature of 37°C, induction with 0.5 mM IPTG concentration, and expression for 3 hours.After SDS-PAGE gel analysis, we concluded that we successfully expressed all HfsG, HfsH, HfsJ, HfsK, and HfsL proteins from C. crescentus CB2 and CB2A strains. We noticed that HfsJ and HfsL glycosyltransferases were visible in lower quantities compared to the other proteins. Both of these protein expression conditions need to be further investigated and optimized.
HfsK is clearly visible on the right side of the gel (Fig. 2).
Table 1. C. crescentus protein sizes in kDa
| Protein Name | Size (kDa) |
|---|---|
| HfsG | 34 |
| HfsH | 27.9 |
| HfsJ | 34.7 |
| HfsK | 43.3 |
| HfsL | 33.3 |
References
1. Hendrickson, H., & Lawrence, J. G. (2000). Mutational bias suggests that replication termination occurs near the dif site, not at Ter sites. FEMS Microbiology Reviews, 24(2), 177–183. https://doi.org/10.1111/j.1574-6976.2000.tb00539.x
2. Andrews, S. C., Robinson, A. K., & Rodríguez-Quiñones, F. (2004). Bacterial iron homeostasis. Journal of Bacteriology, 186(5), 1438–1447. https://doi.org/10.1128/jb.186.5.1438-1447.2004
3.Rabah, A., & Hanchi, S. (2023). Experimental and modeling study of the rheological and thermophysical properties of molybdenum disulfide-based nanofluids. Journal of Molecular Liquids, 384, 123335. https://doi.org/10.1016/j.molliq.2023.123335
4. Boutte, C. C., & Crosson, S. (2009). Bacterial lifestyle shapes stringent response activation. Journal of Bacteriology, 191(9), 2904-2912. https://doi.org/10.1128/jb.01003-08
5. Mackie, J., Liu, Y. C., & DiBartolo, G. (2019). The C-terminal region of the Caulobacter crescentus CtrA protein inhibits stalk synthesis during the G1-to-S transition. mBio, 10(2), e02273-18. https://doi.org/10.1128/mbio.02273-18
6.Thanbichler, M., & Shapiro, L. (2003). MipZ, a spatial regulator coordinating chromosome segregation with cell division in Caulobacter. Journal of Bacteriology, 185(4), 1432-1442. https://doi.org/10.1128/jb.185.4.1432-1442.2003
7. Chepkwony, N.K. and Brun, Y.V. (2021) ‘A polysaccharide deacetylase enhances bacterial adhesion in high-ionic-strength environments’, iScience, 24(9), p. 103071. doi:10.1016/j.isci.2021.103071.
8. Sprecher, K.S. et al. (2017) ‘Cohesive properties of the Caulobacter crescentus holdfast adhesin are regulated by a novel C-di-GMP effector protein’, mBio, 8(2). doi:10.1128/mbio.00294-17.
9. Hershey, D.M., Fiebig, A. and Crosson, S. (2019) ‘A genome-wide analysis of adhesion in Caulobacter crescentus identifies new regulatory and biosynthetic components for holdfast assembly’, mBio, 10(1). doi:10.1128/mbio.02273-18.
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